The present invention relates generally to the operation of a molten carbonate fuel cell with fuel gas derived from the gasification of coal, and more particularly to such an operation wherein steam and carbon dioxide in the reaction products generated at the anode in the fuel cell by the electricity-producing electrochemical reaction are utilized in a coal or coal char gasifier for endothermically reacting coal or char in the presence of a catalyst for providing the fuel gas.
The utilization of fuel cells in relatively large electrical power generating applications is becoming of increasing interest to the electrical industry. The principal reason for this increased interest is primarily due to recent advancements in fuel cell technology which have given strong indications that electrical power generation by using fuel cells can be achieved at rates which may be highly competitive with many existing electrical power producing technologies.
Of the various types of fuel cells being presently evaluated for possible commercial power production applications, molten carbonate fuel cells appear to be sufficiently developed to be considered a suitable candidate. As with all fuel cells, an electrochemical reaction is utilized in the molten carbonate fuel cell to convert the energy of the reaction of various chemicals directly into electrical energy. In a typical molten carbonate fuel cell there is an anode formed of a suitable material such as porous nickel which is separated from a cathode of a suitable material such as porous nickel oxide by an electrolyte formed of an alkali metal carbonate and mixtures thereof with a suitable material such as LiAlO.sub.2. When the electrolyte is heated by any suitable means to a temperature sufficient to become liquified or in a molten state, the electrochemical reaction in a molten carbonate fuel cell can proceed by the simultaneous delivery of hot hydrogen to the anode and hot carbon dioxide and oxygen to the cathode. Normally, the electrochemical reaction can be effectively achieved in the molten carbonate fuel cell as presently available at a temperature in the range of about 1100.degree. to about 1300.degree. F. and at a pressure greater than atmospheric pressure and in the range of about 1.1 to about 6 atmospheres. The electrochemical reaction in the fuel cell is provided the reaction H.sub.2 +CO.sub.3.sup.= .fwdarw.H.sub.2 O+CO.sub.2 +2e.sup.- at the anode and the reaction O.sub.2 +2CO.sub.2 +4e.sup.- .fwdarw.2CO.sub.3.sup.= at the cathode. These reactions produce H.sub.2 O at the anode while causing a transfer of CO.sub.2 from the cathode to the anode with two Faradays of charge with each mole of CO.sub.2. The reaction products generated during the electrochemical reaction in the molten carbonate fuel cell include the H.sub.2 O, primarily in the form of steam, and CO.sub.2 at the anode. If air is used as the source of the oxygen for the reaction at the cathode some nitrogen will be mixed with the CO.sub.2 in the stream of reactants at the cathode. While the efficiency of the electrochemical reaction for converting the reactant gases to electricity in a molten carbonate fuel cell is relatively high, i.e., in the order of about 80 percent, there is an incomplete conversion of all the reactant gases by the reaction. The energy in the reaction gases discharged from the fuel cell is primarily in the form of heat and must be recovered in order to provide the molten carbonate fuel cell with a level of efficiency which will make it commercially competitive with known electrical power producing systems. Any of several techniques may be utilized to recover the "waste" heat the reaction product gases discharged from the fuel cells. These techniques include the use of bottoming cycles which use boilers for the generation of steam for driving a steam turbine coupled to a generator or another suitable load.
Reactant gases used for the electrochemical reaction in a relatively large scale molten carbonate fuel cell system useful for commercial power production purposes may be provided by one of several techniques. For example, the placing of suitable hydrogen and carbon dioxide producing plants in close proximity to one or more fuel cell systems may be one approach for providing the necessary reactant gases. A more recent approach for supplying the reactant gases believed to be worthwhile for consideration is the utilization of a coal or coal char gasifier for producing fuel gas which contains the H.sub.2 and CO.sub.2 necessary for the electrochemical reaction in a molten carbonate fuel cell. In order to use the gaseous products from a coal gasifier in the fuel cell, essentially all of the particulate material greater than about sub-micron size and the sulfur-bearing compounds must be stripped from the fuel gas. After removing the solid particulate material and sulfur-bearing compounds from the gases the CO.sub.2 and the H.sub.2 must be separated from one another for delivery to the appropriate fuel-cell electrodes. While there are several presently known techniques for removing sulfur-bearing compounds and particulate material from the stream of product gases from a gasifier and for separating hydrogen from carbon dioxide, these techniques must be capable providing these functions without excessively reducing the temperature of the gases to a level less than that required for effecting the electrochemical reaction in the fuel cell and maintaining the electrolyte in a liquid state. A discussion pertaining to the use of fuel gas from a gasifier in as the fuel gas for a molten carbonate fuel cell is set forth in a report entitled, "Analysis of Fuel Cell and Competing Power Plant Designs for Utility Base-Load Applications", Argonne National Laboratory, November 1985. This report is incorporated herein by reference.